This invention relates to an electromagnetic pump, and more particularly, to an electromagnetic pump for fluid transfer in which an electric current is intermittently supplied to a solenoid coil to cause a plunger to be moved to and fro, thereby causing a pair of check valves arranged in a fluid passage to open and close alternately so as to give rise to a pumping action.
The pumping action produced by the use of a pair of check valves produces a pulsating flow at the discharge side of the pump.
Because of this pulsating flow, it is impossible to maintain a constant output pressure. To solve this problem, pressure-regulating mechanism has been employed in parallel with a fuel pasage which is adapted to detect the fluid pressure at the discharge side and to feed back a part of the fluid to the inlet when the pressure detected exceeds a predetermined value. Such pressure-regulating mechanism is disclosed in my Japanese Pat. No. 50-33302.
The pressure-regulating mechanism employed in the aforesaid patent, however, does not suffice to entirely absorb the pulsation at the discharge because the pressure-regulating mechanism only detects the pressure variations at the discharge side of the pump at a position in parallel with the discharge passage.
Furthermore, in conventional electromagnetic pumps of this kind, the check valves are not sufficiently tight to prevent fuel leakage and, hence, escape of fuel through the outlet when the pump is at rest, particularly when the pump is turned upside down and/or there is a pressure head at the inlet port. Such leakage is particularly hazardous.
To solve these problems, in the prior art, an additional electromagnetic valve has been provided in the fuel passage between the outlet of the electromagnetic pump and the nozzle of a burner for spraying fuel discharged from the pump. this additional electromagnetic valve is opened when the pump is in operation, and it is closed when the pump is at rest, thereby preventing the fuel from leaking. With this method, however, it is required to provide an additional electromagnetic valve which in turn requires an additional space for mounting. The cost of the assembly is thus undesirably increased. Still further, to avoid the above shortcomings, another improvement has been proposed, to wit, to use a solenoid coil of the electromagnetic pump to energize the electromagnetic valve. This reduces the space requirements and cost considerably, but makes installation more complicated and requires a resdesign of the pump which, in turn, makes it more difficult to control leakage.